Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$16.54	13.346%	$18.7474	$18.75	$18.75	$18.70
Purchase #2	$62.47	3.413%	$64.6021	$64.60	$64.60	$64.60
Purchase #3	$33.70	10.579%	$37.2651	$37.27	$37.25	$37.30
Purchase #4	$136.39	9.529%	$149.3866	$149.39	$149.40	$149.40
Purchase #5	$134.94	3.667%	$139.8882	$139.89	$139.90	$139.90
Purchase #6	$98.31	5.413%	$103.6315	$103.63	$103.65	$103.60
Purchase #7	$184.98	5.765%	$195.6441	$195.64	$195.65	$195.60
7 purchase totals =	$667.33		$709.1650	$709.17	$709.20	$709.10